1. Field of the Invention
This invention relates to the application of color imagery to a rewritable color surface.
2. Description of the Related Art
Electronic paper is a display technology designed to mimic the appearance of ordinary ink on paper. Unlike conventional backlit flat panel displays, electronic paper displays reflect light like ordinary paper. Many of the technologies can hold text and images indefinitely without using electricity, while allowing the text and images to be periodically updated. Electronic paper may be implemented using different technologies, the most common being electrophoretic ink.
In the simplest implementation of an electrophoretic display, titanium dioxide (titania) particles approximately one micrometer in diameter are dispersed in hydrocarbon oil. A dark-colored dye is also added to the oil, along with surfactants and charging agents that cause the particles to take on an electric charge. This mixture is placed between two parallel, conductive plates separated by a gap of 10 to 100 microns. When a voltage is applied across the two plates, the particles will migrate electrophoretically to the plate bearing the opposite charge from that on the particles. When the particles are located at the front (viewing) side of the display, the display appears white, because light is scattered back to the viewer by the high-index titania particles. When the particles are located at the rear side of the display, the display appears dark, because the incident light is absorbed by the colored dye. If the rear electrode is divided into a number of small picture elements (pixels), then an image can be formed by applying the appropriate voltage to each region of the display to create a pattern of reflecting and absorbing regions. Segmentation of the rear electrode into multiple sub-pixels facilitates modulation techniques to achieve multiple gray levels per pixel. A color display may be implemented using a local dot pattern of color filters or color dyes. Typical color displays may be RGB, CMY or CMYK. Electrophoretic displays are considered prime examples of the electronic paper category because of their paper-like appearance and low power consumption.
E Ink Corporation manufactures i a particular type of electrophoretic display in which the titanium dioxide and black dye are encapsulated in microcapsules suspended in a layer of liquid polymer (see U.S. Pat. No. 6,124,851). The Sony Reader and Amazon Kindle are examples of electronic books that use electrophoretic displays developed by E Ink Corporation. The current Sony Readers and Amazon Kindle use the E Ink Pearl display having a resolution of 600×800 to 600×1024 pixels with 16-level gray scale. The display uses an embedded active matrix TFT (thin film technology) to write the voltages to each pixel to update the display. Electrophoretic displays have a relatively slow refresh rate as compared to LCDs, however once the pixel has been written the voltage can be removed and the pixel state will persist.
The E Ink Triton imaging film is a color active matrix display that is capable of displaying thousands of colors in addition to the 16 levels of monochrome. A thin transparent color filter array (CFA) is added in front of the black and white display. The CFA consists of a red, green blue and white sub-pixel. E Ink envisions applications of the triton imaging film in color eBooks, e Textbooks, eNewspapers and eMagazines and electronic signage.
Xerox® Gyricon™ is a field rotatable bichromal colorant sphere. (see U.S. Pat. Nos. 4,126,854, 4,143,103, 5,389,945 and 5,604,027). Each sphere has a bichromal ball having two hemispheres of contrasting colors, e.g. black and white, red and white, each having different electrical properties. Each ball is enclosed within a spherical shell and a space between the ball and shell is filled with a liquid to form a microsphere so that the ball is free to rotate in response to an electrical field. The microspheres are mixed to form a film. An active matrix array may be used to update the display.
U.S. Pat. No. 6,806,453 to Kent D. Vincent et al. describes a hand-held scan-print device that is scanned over a surface of a paper-like rewritable sheet such as E Ink's film or Xerox® Gyricon™. The sheet has a colorant responsive to a linear array of pixel-sized electric fields written over the sheet by the scan-print device during each scan, producing a bistable pixel (e.g., black or white) in response to field polarity. A scanning navigation subsystem positions the black and white data on the sheet (See U.S. Pat. No. 5,825,044 to Allen et al.). Once a series of scans sufficient to cover the entire sheet has been made, the printed image appears as if printed conventionally. The print remains stable until reprinted or intentionally erased.